US2442189A

US2442189A - Flash control system

Info

Publication number: US2442189A
Application number: US639127A
Authority: US
Inventors: Spencer L Bellinger
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1946-01-04
Filing date: 1946-01-04
Publication date: 1948-05-25
Anticipated expiration: 1965-05-25

Description

May 25, 1948. s. BELLINGER 2,442,189

FLASH CONTROL SYSTEM Fiied Jan. 4, .1946

Fig. 2 sfgkl/aa Inventor: Spencer" Lfiellinger,

H i s Attorney.

Patented MI! 2 1948 UNITED STATES PATENT OFFICE FLASH CONTROL SYSTEM Spencer L. Bcllinger, Lake Luzerne, N. Y., assignor to General Electric Company, a corporation of New York Application January 4, 194.6, Serial No. 639,127

4 Claims. (Cl. 320-1) 1 2 This invention relates to control systems, more a voltage drop which is less than the breakdown particularly to systems for producing illuminating voltage of the gap with which it is connected in flashes. and it has for an object the provision of parallel. A suitable electric valve and current a simple, reliable, inexpensive and improved syslimiting resistance are connected in parallel with tem of this character. 5 one of the portions of the divider and its corre- In the study and analysis of high speed mesponding gap. This valve serves to initiate the chanical motions there is need for means for breakdown of the gap in such a manner that a photographing these motions in a period or time flash-producing discharge takes place across both which is sufllciently short to freeze the megaps. chanical action. For example, in the making of For a better and more complete understanding shadowgraph photographs of objects and gases, of the invention, reference should now be had to the object or gas is frequently moving at a speed the following specification and to the accompanyin excess of the speed of sound and sometimes at ing drawing of which Fig. 1 is a simple, diagram- 9. speed as high as 3000 ft. per second. In order matical illustration of an embodiment of the to freeze motion at this speed, an illuminating ll invention, and Fig. 2 is a diagram which illusflash of extremely brief duration is required, and trates the physical arrangement of the spark accordingly a further object 0! this invention is gaps with respect to the capacitor. the provision of a system for producing an 11- Referring now to the drawing, a capacitor i is luminating flash of which the photographically arranged to be charged from a suitable D.-C. eflective duration is a fraction of a microsecond. source, such as represented by the positive supply Another object is the provision of a flash conline 2 and the negative supply line 3. A resistor trol system having no electric valves in the fiash- 4 is connected in series between the positive line producing discharge circuit but in which the dis- 2 of the source and the positive terminal of the charge. circuit is controlled by means of an eleccapacitor for limiting the charging current. A tric valve. voltage divider comprising resistors 5, 6, and "I is One advantage of the arrangement in which no connected across the source. In a typical case electric valve is included in the discharge circuit the voltage of the source 2-3 may be assumed is that the high resistance of such electric valve to be 15,000 volts. It may also be assumed that is eliminated. This results in a very substantial the capacitor I has a capacitance of .12 mid. and sh t nin of t a t al du at of th discharge so that it is to be charged to a voltage of 14,900 volts. and the duration of the photographically effective Accordingly the capacitor l is connected to points portion of the discharge. 5a and 6b on-the voltage divider having a po- Still another object of the invention is the protential diiference of 14,900 volts. The supply convision of a flash control system in which the enductor 3 is connected to ground. The voltage closed area of the spark discharge circuit loop drop between the point 61) of the voltage divider and its inductance are reduced to a. minimum. and the lower terminal la is such a small amount In carrying the invention into effect in one form that for allpractical purposes the lower plate of thereof, a capacitor is provided together with a the capacitor i is effectively connected to ground. source of unidirectional voltage for charging the As shown in Fig. 2, the capacitor is mounted capacitor to a desired predetermined voltage. A within a suitable enclosure 8 upon which is pair of spark discharge gaps are connected in mounted an insulating bushing 8'. A pair of series directly across this capacitor. The gaps spark gaps 9 and I 0 are connected in series reare of such dimension that the combined breaklationship directly across the capacitor. The down voltage is substantially in excess of the electrode 9a of gap '9 is directly connected to the predetermined voltage to which the capacitor is positive terminal la of the capacitor which is charged and the breakdown voltage of each gap brought out through the insulating bushing 8'.

individually is substantially less than this prede- The electrode 9b of gap- 9 and electrode i0a of termined voltage. In addition, a voltage divider gap iii are directly connected together by means comprising a relatively high resistance is conof a short, heavy conductor II and may be connected in parallel with the capacitor and the sidered as comprising a single central electrode. gaps. A connection from an intermediate point The remaining electrode lb of gap Ill is directly on the divider to the central electrode of the gap connected to the lower ground terminal of the is provided so that each of the gaps is paralleled capacitor. 4

by an equal portion of the voltage divider resist- The junction point 61: of the two resistors 5 and ance. Each of these portions of the divider has ,0 Ii is connected to the short conductor ii and is thus connected to the central electrode .01 the two spark gaps.

Although the resistance of the resistors 5 and 6 may be any suitable value, it is preferably relatively high. In a typical case the resistors 5 and 6 may each have a resistance of 100 megohms. Thus, with the capacitor I charged to a voltage of 14,900 volts, current flowing through the voltage divider is .0000745 ampere and the voltage drop across each resistor is 7,450 volts.

The gaps should have a combined breakdown voltage which is substantially greater than the predetermined voltage to which the capacitor I is charged and should have an individual breakdown voltage which is substantially greater than the voltage drop across the portion of the voltage divider with which it is connected in parallel. Thus, the electrodes of the gaps are properly set with a spacing such that neither gap will break down with a voltage of 7,450 volts supplied across it. For the constants assumed for the capacitor I and the resistors 5 and B, a proper spacing of the electrodes would provide an individual breakdown voltage of 8,500 volts for each gap.

In parallel with the resistor 6 is connected 9. suitable electric valve I2. Although this electric valve may be of any suitable type it is preferably a, thyratrcn. The anode I'Za of the thyratrcn is connected through a suitable resistor I 3 to the point 6a of the voltage divider, and the cathode I2?) is directly connected to the negative terminal 8b of the resistor 6. The grid I2c of the thyratron is connected by means of a conductor I4 to the grounded terminal la 01' the voltage divider and thus the grid is maintained at a voltage which is negative with respect to the voltage of the cathode by the amount of the voltage between the points 6b and 1a of the voltage divider. In a typical case the resistor I3 may suitably have a resistance of .1 megohm.

For the purpose of initiating conduction of the thyratrcn, a capacitor I5 is provided having one terminal connected to the cathode I2b together with a manually operated switching device I6 for connecting the other terminal of the capacitor to ground. A resistor I1 is connected in parallel with the capacitor I5.

With the foregoing understanding of the elements and their organization, the operation of the system itself will be readily understood from the following detailed description. When the

conductors

2 and 3 are energized, the capacitor I is charged up to a voltage which was assumed to be 14,900 volts. The voltage across each of gaps 9 and I is 7,450 volts which is less than the breakdown voltage of each gap. Consequently, no discharge takes place across the gaps.

The voltage of the grid I20 of the thyratrcn is maintained approximately 100 volts negative with respect to the voltage of the cathode in order to maintain the valve non-conducting when the switch I6 is open.

The discharge across the gaps 9 and I0 is initiated by closing the switch I 6 to connect the lower terminal of the capacitor I to ground. Since ihe capacitor l5 cannot charge instantly, the voltage of the upper plate follows that of the lower plate, i. e. for a brief instant it has ground potential and thus the voltage of the cathode I21) 18 lowered sufficiently with respect to the voltage of the grid to render the thyratrcn conducting.

Since the resistor 5 has a very high resistance, I g. 100 megohms, the current conducted through i resistor I3 and the thyratron I2 produce such a lar e voltage drop across the resistor 5 t at the potential or the point a approaches ground potential. Thus, the voltage applied across the gap 9 is nearly 14,900 volts which is substantially in excess of its breakdown voltage. Consequently, the gap breaks down but the current flow across the gap 0 is limited by the resistor I3 to .15 ampere. However, this current flowing through the resistor I3 produces a voltage drop across the resistor of approximately 14,900 volts and thus the voltage across the gap I0 is raised to approximately 14,900 volts which is in excess of the breakdown voltage. Consequently, the discharge circuit from the positive terminal of the capacitor I is completed through the gaps 9 and I0 to ground and the discharge produces a brilliant flash of extremely brief photographically efl'ective duration, e. g. approximately microsecond. Since the major light output of either gap cannot occur until the other gap has broken down to permit the heavy surge of current to flow, there is no effective time lag between the peak emissions of light in the two gaps.

After the discharge across the gaps takes place, the voltage of the anode of the thyratron is reduced to such a lo'w value that conduction is extinguished. Following the closing of the switch IS, the capacitor I5 is charged and thus the voltage of the cathode I2b regains its former value which is positive with respect to the voltage of the grid I 2c. Thus, the flash cannot be repeated until the starting switch IE is opened to permit the capacitor I5 to discharge through resistor I1 and to leave the system in a reset condition.

Although in accordance with the provisions of the atent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it is to be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims. 5

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A flash producing system comprising a capacitor, means for charging said capacitor to a predetermined voltage, means providing a pair of spark discharge gaps connected in series across said capacitor and having a, combined breakdown voltage substantially greater than said predetermined voltage, a. voltage divider comprising a resistor of relatively high resistance connected in parallel with said capacitor and having a first portion connected in parallel with a first one of said gaps and a second portion connected in parallel with the second of said gaps, each of said portions having a voltage drop substantially less than the breakdown voltage of the parallel gap, means comprising an electric valve connected in parallel with said first portion for effecting an initial discharge across said second gap, and a resistance included in the anode-cathode circuit of said valve for limiting said initial discharge to a value insuflicient to produce an eliective flash and for increasing the voltage across said first gap above its breakdown voltage thereby to effect a main discharge across both said gaps.

2. A flash producing system comprising a capacitor, means for charging said capacitor to a predetermined voltage, means providing a pair of spark discharge gaps connected in series across said capacitor and having a combined breakdown voltage substantially greater than said predetermined voltage and having individual breakdown voltages substantially less than said predetermined voltage, a voltage divider comprising a resistor having a'relatively high resistance con-- nected across said capacitor and having a first portion connected in parallel with a first of said aps and a second portion in parallel with the second of said gaps, a normally non-conducting electric valve having its. anode-cathode circuit connected in parallel with said second gap and said second divider portion, a current limiting resistance connected in the anode-cathode circuit of said valve, and means for rendering said valve conducting to increase the voltage across said first gap above its breakdown voltage to initiate a relatively slow rate discharge across said first gap and thereby increase the voltage across said second gap above its breakdown value to eiIect a relatively high rate discharge across both said gaps.

3. A flash producing system comprising a capacitor, means for charging said capacitor to a predetermined voltage, means providing a pair of spark discharge gaps connected in series across said capacitor and having a combined breakdown voltage substantially greater than said predetermined voltage, a voltage divider comprising a resistor of relatively high resistance connected in parallel with said capacitor and having a first portion connected in parallel with a first one of said gaps and a second portion connected in parallel'with the second of said gaps, each of said portions having a voltage drop substantially less than the breakdown voltage or the parallel gap, a normally non-conducting electric valve having its anode-cathode circuit connected in parallel with said first portion, means for rendering said valve conducting to eiiect an initial discharge across said second gap. and a resistance included in said anode-cathode circuit for limiting said initial discharge to a value insufllcient to produce an efiective fiash and for increasing the voltage across said first gap above its breakdown voltage to complete a main discharge path and eiiect a main discharge through both said gaps.

4. A flash producing system comprising a main 6 capacitor, means for charging said capacitor to a predetermined voltage comprising a pair of supply conductors, a voltage divider connected across said conductors comprising a relatively high resistance connectedacross said capacitor and a relatively low resistance, means providing a pair or spark discharge gaps connected in series across said capacitor and having a combined breakdown voltage substantially greater than said predetermined voltage and each of said gaps having a breakdown voltage substantially less than said predetermined voltage, a connection from an intermediate point of said high resistance 0! said divider to anintermediate point in the circuit between said gaps so that each 01' said gaps is paralleled by a diiierent portion or said high resistance, an electric valve provided with an anode, a cathode and a control grid and having its anode cathode circuit connected in parallel with a first one of said gaps and the corresponding portion of said high resistance, a connection from the grid of said valve to a point on said,

divider having a voltage that is negative with respect to the point of connection of said cathode, means for rendering said valve conducting to increase the voltage across the second of said gaps above its breakdown value to eiiect an initial nnrsanucns crrr-m The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Seeley Oct. 19, 1915 Number